Michel Van Camp

Royal Belgian Institute of Natural Sciences

Evapotranspiration (ET) controls the flux between the land surface and the atmosphere. Assessing the ET ecosystems remains a key challenge in hydrology. We have found that the ET water mass loss can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution of wat...

How and why does gravity vary? Why do we measure it? How do we measure gravity?

We estimate the signature of the climate-induced mass transfers in repeated absolute gravity measurements based on satellite gravimetric measurements from the GRACE mission. We show results at the globe scale, and compare them with repeated absolute gravity (AG) time behavior in three zones where AG surveys have been published: Northwestern Europe,...

[The definitive version is available at www.blackwell-synergy.com, http://dx.doi.org/10.1093/gji/ggt524] Recent studies show that terrestrial and space based observations of gravity agree over Europe. In this paper, we compare time series of terrestrial gravity (including the contribution due to surface displacement) as measured by superconducting...

In continental plate interiors, ground surface movements are at the limit of the noise level and close to or below the accuracy of current geodetic techniques. Absolute gravity measurements are valuable to quantify slow vertical movements, as this instrument is drift free and, unlike GPS, independent of the terrestrial reference frame. Repeated abs...

This study provides a quantitative approach to search for mantle plumes in global seismic tomography models without any preconceived notions about the associated mantle velocity anomalies, other than the assumption that the plumes are not significantly deflected horizontally by more than 6○, anywhere in the mantle. We design identification tests wi...

Understanding and modelling the properties of the stochastic variations in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the increasing span of geodetic time series, it is expected that additional observations wou...

Understanding and modelling the properties of the stochastic variability -- often referred to as noise -- in geodetic time series is crucial to obtain realistic uncertainties for deterministic parameters, e.g., long-term velocities, and helpful in characterizing non-modelled processes. With the ever-increasing span of geodetic time series, it is ex...

We employ the barotropic, data-unconstrained ocean tide model TiME to derive an atlas for degree-3 tidal constituents including monthly to terdiurnal tidal species. The model is optimized with respect to the tide gauge data set TICON-td that is extended to include the respective tidal constituents of diurnal and higher frequencies. The tide gauge v...

We investigate the potential of causal inference methods (CIMs) to reveal hydrological connections from time series. Four CIMs are selected from two criteria, linear or nonlinear and bivariate or multivariate. A priori, multivariate, and nonlinear CIMs are best suited for revealing hydrological connections because they fit nonlinear processes and d...

Extreme events will become more common due to global change, requiring enhanced monitoring and pushing conventional observation networks to their limits. This encourages us to combine all the possible sources of information to obtain a complete picture of extreme events and their evolution. This commentary builds on an example of the July 2021 cata...

Applying new technology rooted in quantum mechanics and relativity to terrestrial and space geodesy will sharpen our understanding of how the planet responds to natural and human-induced changes.

Applying new technology rooted in quantum mechanics and relativity to terrestrial and space geodesy will sharpen our understanding of how the planet responds to natural and human-induced changes.

Monitoring vertical land motions (VLMs) at the level of 0.1 mm/yr remains one of the most challenging scientific applications of global navigation satellite systems (GNSS). Such small rates of change can result from climatic and tectonic phenomena, and their detection is important to many solid Earth‐related studies, including the prediction of coa...

The LASUGEO project: monitoring LAnd SUbsidence caused by Groundwater exploitation through gEOdetic measurements.-PS-InSAR (Interferometric Synthetic Aperture Radar) data allow measuring slow-moving ground deformations with high spatial resolution.-In Belgium, most of the subsidence is related to fluctuations of water pressure in aquifers (Figure 1...

We investigate the potential of causal inference methods (CIMs) to reveal hydrological connections from time-series. Four CIMs are selected from two criteria, linear or nonlinear, and bivariate or multivariate. A priori, multivariate and nonlinear CIMs are best suited for revealing hydrological connections because they suit nonlinear processes and...

Global seismic tomography has greatly progressed in the past decades, with many global Earth models being produced by different research groups. Objective, statistical methods are crucial for the quantitative interpretation of the large amount of information encapsulated by the models and for unbiased model comparisons. Here we propose using a rota...

Over the past two decades, numerous studies demonstrated that the stochastic variability in GNSS position time series – often referred to as noise – is both temporally and spatially correlated. The time correlation of this stochastic variability can be well approximated by a linear combination of white noise and power-law stochastic processes with...

Global seismic tomography has greatly progressed in the past decades, with many global Earth models being produced by different research groups. Objective, statistical methods are crucial for the quantitative interpretation of the large amount of information encapsulated by the models as well as for unbiased model comparisons. We propose here to us...

One main application of electrical resistivity tomography (ERT) is the non-invasive detection of geological or hydrological structures in the shallow subsurface. This paper investigates the capability of time-series clustering to retrieve such features on real time-lapse ERT datasets considering three aspects: (1) the comparison between three clust...

Please cite this article as: D. Delforge, A. Watlet, O. Kaufmann, et al., Time-series clustering approaches for subsurface zonation and hydrofacies detection using a real time-lapse electrical resistivity dataset, Journal of Applied Geophysics (2020), https://doi. Abstract One main application of electrical resistivity tomography (ERT) is the non-i...

Spring-based gravimeters are light and easy to install, with a precision around 5 μGal/√Hz. However, they are still not used for long-term gravity monitoring. The main reason for that is the non-linear drift of those instruments, which is very difficult to correct without removing geophysical signals. We will show that when the tilt is actively con...

Flash flood events are expected to become increasingly common with the global increases in weather extremes. They are a significant natural hazard that affects karst landscapes, which host large resources of drinking water worldwide. The role played by underground flood events in the karst aquifer recharge is complex due to the heterogeneity of the...

For more than a century, the study of streamflow recession has been dominated by seemingly physically‐based parametric methods that make assumptions on the nonlinear nature of the hydrograph recession. In practice, several studies have shown that various degrees of nonlinearity occur in the same time‐series and that parametric methods can underfit...

The regional key comparison of absolute gravimeters, EURAMET.M.G-K3 and the simultaneously organized additional comparison, was held in Germany at the Geodetic Observatory Wettzell of the German Federal Agency for Cartography and Geodesy in the spring of 2018. Here we present the list of the participants who actually performed measurements during t...

This study proposes a method for the cross calibration of tide gauges. Based on the combination of at least three collocated sea level time series, it takes advantage of the least squares variance component estimation (LS-VCE) method to assess both sea level biases and uncertainties in real conditions. The method was applied to a multi-instrument e...

Data and metadata products based on intensive terrestrial gravity measurements covering the Belgian territory have been established compliant to the new ISO19115‐1 profile for gravity‐related data. A short historical introduction on gravity measurements on the Belgian territory is presented, starting with the first gravity measurement in 1892. This...

The radar-based estimation of intense precipitation produced by convective storms is a challenging task and the verification through comparison with gauges is questionable due to the very high spatial variability of such types of precipitation. In this study, we explore the potential benefit of using a superconducting gravimeter as a new source of...

On Friday November 16, 2018, the kilogram will join its fellow metric units with a definition based on fundamental physical constants, but these units maintain links to their roots in the geosciences.

Studies about sea level change at the coast require high quality sea level time series. The main source of sea level measurements is presently provided by digital coastal tide gauges. Calibration campaigns are regularly carried out to ensure their precisions & accuracies. Several types of sea level sensors exist – tide pole, probe, radar tide gauge...

Recharge processes of karst aquifers are difficult to assess given their strong heterogeneity and the poorly known effect of vadose zone on infiltration. However, recharge assessment is crucial for the evaluation of groundwater resources. Moreover, the vulnerability of karst aquifers depends on vadose zone behavior since it is the place where most...

Water infiltration and recharge processes in karst systems are complex and difficult to measure with conventional hydrological methods. In particular, temporarily saturated groundwater reservoirs hosted in the vadose zone can play a buffering role in water infiltration. This results from the pronounced porosity and permeability contrasts created by...

Superconducting gravimeter at Belgium’s Membach geophysical station set a new record for monitoring gravitational fluctuations caused by storm surges, groundwater fluctuations, and the Moon’s tidal pull.

A recent article in Reviews of Geophysics examined terrestrial techniques for measuring changes in gravity over time and their application to the geosciences.

In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field.Time-variable gravity, because of its high accuracy...

Water infiltration and recharge processes in karst systems are complex and difficult to measure with conventional hydrological methods. Especially, temporarily saturated groundwater reservoirs hosted in the vadose zone can play a buffering role in water infiltration. This results from the pronounced porosity and permeability contrasts created by lo...

In the framework of the regional EURAMET.M.G-K2 comparison of absolute gravimeters, 17 gravimeters were compared in November 2015. Four gravimeters were from different NMIs and DIs, they were used to link the regional comparison to the CCM.G.K2 by means of linking converter. Combined least-squares adjustments with weighted constraint was used to de...

Present knowledge of karst systems has evidenced the importance of the vadose zone on the water dynamics. Temporary perched aquifers can appear in the subsurface, especially in the epikarst layer, due to changes of weather conditions, reduced evapotranspiration and the vertical gradients of porosity and permeability. Seasonal water variations in th...

The role of the vadose zone in karst aquifers is under the scope of the multidisciplinary project KARAG (www.karag.be). This paper shortly describes an innovative methodology to highlight transfer and storage characteristics of the unsaturated zone. This long term and multi-scale methodology was applied in two karstic areas in southern Belgium. Fir...

The vadose zone of karst systems plays an important role on the water dynamics. In particular, temporary perched aquifers can appear in the subsurface due to changes of weather conditions, reduced evapotranspiration and the vertical gradients of porosity and permeability. Although many difficulties are usually encountered when studying karst enviro...

Analysing independent 1-yr data sets of 10European superconducting gravimeters (SG) reveals statistically significant temporal variations of M2 tidal parameters. Both common short-term (<2 yr) and long-term (>2 yr) features are identified in all SG time-series but one. The averaged variations of the amplitude factor are about 0.2 per mille. The pat...

The vadose zone of karst systems plays an important role on the water dynamics. In particular, temporary perched aquifers can appear in the subsurface due to changes of climate conditions, diminished evapotranspiration and differences of porosity relative to deeper layers. It is therefore crucial, but challenging, to separate the hydrological signa...

This paper reports on different sources of errors that occur in the calibration process of a superconducting gravimeter (SG), determined by comparison with a ballistic absolute gravimeter (AG); some of them have never been discussed in the literature. We then provide methods to mitigate the impact of those errors, to achieve a robust calibration es...

Hydrogeophysical tools allow characterizing the heterogeneity of karsts and evidencing groundwater storage in their subsurface. A permanent gravimetric monitoring highlights seasonal variations in gravity that can be related to vadose zone effects after the discrimination of the saturated zone signature with direct measurements. A surface ERT monit...

In November 2013 an International Key Comparison, CCM.G-K2, was organized in the Underground Laboratory for Geodynamics in Walferdange. The comparison has assembled 25 participants coming from 19 countries and four different continents. The comparison was divided into two parts: the key comparison that included 10 NMIs or DIs, and the pilot study i...

The very coarse network of SG stations does not allow sampling enough the regional scale so that anything can really be learned out of the SG that can be useful for GRACE study. There are no reasons why they should look alike, and, actually, they do not: nothing is strange about that result. We deeply regret that the comment by Crossley et al. (201...

Through the use of three different geophysical techniques, we highlight structures and groundwater storage changes in the subsurface of a karst system, in the so-called epikarst layer. An Electrical Resistivity Tomography (ERT) has been installed onsite informing on conductivity variations directly related to changes in groundwater content within t...

Gravimetric time series can provide vital clues about subsurface dynamics associated with active volcanism. Here, we report on continuous and campaign-style gravimetric observations on Montserrat between 2006 and 2009. More than 240 days of continuous gravimetric records enabled us to derive a first local joint solid Earth tides and ocean loading m...

Spécial tremblement de Terre de Liège du 8 novembre 1983: trente ans après: le réseau belge de surveillance sismique depuis 1985.

This paper investigates the precision of the estimation of geophysical fluid load deformation computed from GRACE space gravity, GPS vertical displacement and geophysical fluids models [Global Circulation Models (GCMs) for ocean, atmosphere and hydrology], using the three-cornered hat method. This method allows the estimation of the variance of the...

Geodetic measurements above subduction zones have revealed a range of transient deformations. The mechanism by which slow slips occur remains uncertain. In particular, does surface deformation represents the integrated deformation from a large number of discrete seismic slip events? Moreover, little is known about displacements of materials having...

The level of the Victoria Lake is analysed using space gravity and altimetry data, together with the output of the large-scale land LaD water model. The good agreement between the space gravity and altimetry proves the robustness of the results. Comparing these geodetic observations with the LaD land water model allows one to better estimate the re...

Cet article décrit les principaux mécanismes en œuvre en zones de subduction, où de gigantesques portions de plaques tectoniques plongent sous d'autres, générant une large panoplie de séismes et de déformations de la croûte terrestre. En particulier, ces zones peuvent produire les plus grands séismes connus (magnitude supérieure à 9), ainsi que des...

We propose a method to evaluate the stress generated at the local scale by the spatial variations of the Gravitational Potential Energy (GPE), which is related to inhomogeneous topography and mass distribution in the lithosphere. We show that it is possible to infer these local stress sources from the second spatial derivatives of a geoid height gr...

Electrical resistivity tomography (ERT) monitoring experiments are being conducted more often to image spatiotemporal changes in soil properties. When conducting long-term ERT monitoring, the identification of suspicious electrodes in a permanent spread is of major importance because changes in electrode contact properties of a single electrode may...

This paper evaluates different data-processing methods to determine the gravity rate of change, using repeated absolute gravimeter (AG) measurements and continuous monitoring by a superconducting gravimeter (SG). Based on synthetic data representative of signals observed by SGs at various station locations, we demonstrate that the addition of SG in...

During long-term ERT monitoring experiments, the data quality may reveal time-dependent mainly due to changes in galvanic contact resistance between buried electrodes and soil. Identifying suspicious electrodes in a permanent spread is of major importance as a faulty electrode may affect the quality of tens to hundreds of measurements on each time-...

Vulcanian eruptions form a continuum ranging from the weaker Strombolian-type to violent sub-Plinian activity. They are short-lived (tens of seconds to tens of minutes) events commonly associated with a Volcanic Eruption Index (VEI) of 2-3. Extrusion of viscous magma and the formation of a lava dome is often interspersed by short-lived vigorous (Vu...

Most often, vertical ground movements are at the limit of the noise level and close to or below the accuracy of current geodetic techniques. Absolute gravity measurements are valuable to quantify slow vertical movements, as this instrument is drift free and, unlike GPS, independent of the terrestrial reference frame. On the other hand, for logistic...

An absolute gravimeter allows us to determine the local value of gravity, which makes its accuracy assessment challenging. The instrumental offsets are classically estimated by performing comparisons of the results obtained by a set of instruments measuring at the same location but at different epochs (measuring at the same place and epoch is physi...

The Bureau International des Poids et Mesures (BIPM), Sèvres, France, hosted the 7th International Comparison of Absolute Gravimeters (ICAG) and the associated Relative Gravity Campaign (RGC) from August to September 2005. ICAG 2005 was prepared and performed as a metrological pilot study, which aimed: • To determine the gravity comparison referen...

Extrusion of viscous magma and the subsequent formation of a lava dome is often interspersed by short-lived vigorous (Vulcanian) explosions. The causes for and the timing of the transition from effusive to explosive activity during dome formation are poorly understood and forecasting this transition remains a challenge. Here, we describe and interp...